Control system and method for a dual clutch transmission

ABSTRACT

A hydraulic control system and method for controlling a dual clutch transmission includes a plurality of pressure and flow control devices and logic valve assemblies in fluid communication with a plurality of clutch actuators and with a plurality of synchronizer actuators. The clutch actuators are operable to actuate a plurality of torque transmitting devices and the synchronizer actuators are operable to actuate a plurality of synchronizer assemblies. Selective activation of combinations of the pressure control solenoids and the flow control solenoids allows for a pressurized fluid to activate at least one of the clutch actuators and synchronizer actuators in order to shift the transmission into a desired gear ratio.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.61/421,136, filed Dec. 8, 2010. The entire contents of the aboveapplication are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a control system and method for a dual clutchtransmission, and more particularly to an electro-hydraulic controlsystem and method having a plurality of solenoids and valves operable toactuate a plurality of actuators within the dual clutch transmission.

BACKGROUND

A typical multi-speed, dual clutch transmission uses a combination oftwo friction clutches and several dog clutch/synchronizers to achieve“power-on” or dynamic shifts by alternating between one friction clutchand the other, with the synchronizers being “pre-selected” for theoncoming ratio prior to actually making the dynamic shift. “Power-on”shifting means that torque flow from the engine need not be interruptedprior to making the shift. This concept typically uses countershaftgears with a different, dedicated gear pair or set to achieve eachforward speed ratio. Typically an electronically controlled hydrauliccontrol circuit or system is employed to control solenoids and valveassemblies. The solenoid and valve assemblies actuate clutches andsynchronizers to achieve the forward and reverse gear ratios.

While previous hydraulic control systems are useful for their intendedpurpose, the need for new and improved hydraulic control systemconfigurations within transmissions which exhibit improved performance,especially from the standpoints of efficiency, responsiveness andsmoothness, is essentially constant. Accordingly, there is a need for animproved, cost-effective hydraulic control system for use in a dualclutch transmission.

SUMMARY

A method for controlling a hydraulic control system is provided. Thehydraulic control system includes a plurality of pressure and flowcontrol devices and logic valves in fluid communication with a pluralityof clutch actuators and with a plurality of synchronizer actuators. Theclutch actuators are operable to actuate a plurality of torquetransmitting devices and the synchronizer actuators are operable toactuate a plurality of synchronizer assemblies. Selective activation ofcombinations of the pressure control solenoids and the flow controlsolenoids allows for a pressurized fluid to activate at least one of theclutch actuators and synchronizer actuators in order to shift thetransmission into a desired gear ratio.

In one example of the hydraulic control system, the hydraulic controlsystem includes an electric pump and an accumulator that provide apressurized hydraulic fluid.

In another example of the hydraulic control system, the hydrauliccontrol system includes two pressure control devices and two flowcontrol devices used to actuate the dual clutch.

In yet another example of the hydraulic control system, the hydrauliccontrol system includes two pressure control devices, two flow controldevices, and two logic valves and a logic valve control solenoid used toactuate the plurality of synchronizer assemblies.

Further features, aspects and advantages of the present invention willbecome apparent by reference to the following description and appendeddrawings wherein like reference numbers refer to the same component,element or feature.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic diagram of an exemplary dual clutch transmissionhaving a hydraulic control system according to the principles of thepresent invention;

FIGS. 2A-B are schematic diagrams of an embodiment of a hydrauliccontrol system for a dual clutch transmission according to theprinciples of the present invention;

FIG. 3 is a flow chart illustrating a method of controlling a hydraulicfluid delivery subsystem within the hydraulic control system;

FIG. 4 is a chart illustrating accumulator pressure over time;

FIG. 5 is a flow chart illustrating a method of controlling a clutchactuator subsystem within the hydraulic control system;

FIG. 6 is a flow chart illustrating a method of controlling asynchronizer actuator subsystem within the hydraulic control system; and

FIG. 7 is a chart illustrating synchronizer controls over time.

DESCRIPTION

With reference to FIG. 1, an exemplary dual clutch automatictransmission incorporating the present invention is illustrated andgenerally designated by the reference number 10. The dual clutchtransmission 10 includes a typically cast, metal housing 12 whichencloses and protects the various components of the transmission 10. Thehousing 12 includes a variety of apertures, passageways, shoulders andflanges which position and support these components. While the housing12 is illustrated as a typical rear wheel drive transmission, it shouldbe appreciated that the transmission 10 may be a front wheel drivetransmission or a rear wheel drive transmission without departing fromthe scope of the present invention. The transmission 10 includes aninput shaft 14, an output shaft 16, a dual clutch assembly 18, and agear arrangement 20. The input shaft 14 is connected with a prime mover(not shown) such as an internal combustion gas or Diesel engine or ahybrid power plant. The input shaft 14 receives input torque or powerfrom the prime mover. The output shaft 16 is preferably connected with afinal drive unit (not shown) which may include, for example, propshafts,differential assemblies, and drive axles. The input shaft 14 is coupledto and drives the dual clutch assembly 18. The dual clutch assembly 18preferably includes a pair of selectively engageable torque transmittingdevices including a first torque transmitting device 22 and a secondtorque transmitting device 24. The torque transmitting devices 22, 24are preferably dry clutches. The torque transmitting devices 22, 24 aremutually exclusively engaged to provide drive torque to the geararrangement 20.

The gear arrangement 20 includes a plurality of gear sets, indicatedgenerally by reference number 26, and a plurality of shafts, indicatedgenerally by reference number 28. The plurality of gear sets 26 includesindividual intermeshing gears that are connected to or selectivelyconnectable to the plurality of shafts 28. The plurality of shafts 28may include layshafts, countershafts, sleeve and center shafts, reverseor idle shafts, or combinations thereof. It should be appreciated thatthe specific arrangement and number of the gear sets 26 and the specificarrangement and number of the shafts 28 within the transmission 10 mayvary without departing from the scope of the present invention. In theexample provided, the transmission 10 provides seven forward gears and areverse gear.

The gear arrangement 20 further includes a first synchronizer assembly30A, a second synchronizer assembly 30B, a third synchronizer assembly30C, and a fourth synchronizer assembly 30D. The synchronizer assemblies30A-D are operable to selectively couple individual gears within theplurality of gear sets 26 to the plurality of shafts 28. Eachsynchronizer assembly 30A-D is disposed either adjacent certain singlegears or between adjacent pairs of gears within adjacent gear sets 26.Each synchronizer assembly 30A-D, when activated, synchronizes the speedof a gear to that of a shaft and a positive clutch, such as a dog orface clutch. The synchronizer positively connects or couples the gear tothe shaft. The synchronizer actuator is bi-directionally translated by ashift rail and fork assembly (not shown) within each synchronizerassembly 30A-D.

The transmission also includes a transmission control module 32. Thetransmission control module 32 is preferably an electronic controldevice having a preprogrammed digital computer or processor, controllogic, memory used to store data, and at least one I/O peripheral. Thecontrol logic includes a plurality of logic routines for monitoring,manipulating, and generating data. The transmission control module 32controls the actuation of the dual clutch assembly 18 and thesynchronizer assemblies 30A-D via a hydraulic control system 100according to the principles of the present invention.

Turning to FIGS. 2A-B, the hydraulic control system 100 generallyincludes three subsystems: an oil or hydraulic fluid delivery subsystem100A, a clutch actuator subsystem 100B, and a synchronizer actuatorsubsystem 100C. The hydraulic control system 100 is operable toselectively engage the dual clutch assembly 18 and the synchronizerassemblies 30A-D by selectively communicating a hydraulic fluid 102 froma sump 104 to a plurality of shift actuating devices, as will bedescribed in greater detail below. The sump 104 is a tank or reservoirto which the hydraulic fluid 102 returns and collects from variouscomponents and regions of the automatic transmission 10. The hydraulicfluid 102 is forced from the sump 104 via a pump 106. The pump 106 isdriven by an electric motor or combustion engine (not shown) or anyother type of prime mover. The pump 106 may be, for example, a gearpump, a vane pump, a gerotor pump, or any other positive displacementpump. The pump 106 includes an inlet port 108 and an outlet port 110.The inlet port 108 communicates with the sump 104 via a suction line112. The outlet port 110 communicates pressurized hydraulic fluid 102 toa supply line 114. The supply line 114 is in communication with a springbiased blow-off safety valve 116, a pressure side filter 118, and aspring biased check valve 120. The spring biased blow-off safety valve116 communicates with the sump 104. The spring biased blow-off safetyvalve 116 is set at a relatively high predetermined pressure and if thepressure of the hydraulic fluid 102 in the supply line 114 exceeds thispressure, the safety valve 116 opens momentarily to relieve and reducethe pressure of the hydraulic fluid 102. The pressure side filter 118 isdisposed in parallel with the spring biased check valve 120. If thepressure side filter 118 becomes blocked or partially blocked, pressurewithin supply line 114 increases and opens the spring biased check valve120 in order to allow the hydraulic fluid 102 to bypass the pressureside filter 118.

The pressure side filter 118 and the spring biased check valve 120 eachcommunicate with an outlet line 122. The outlet line 122 is incommunication with a second check valve 124. The second check valve 124is in communication with a main supply line 126 and is configured tomaintain hydraulic pressure within the main supply line 126. The mainsupply line 126 supplies pressurized hydraulic fluid to an accumulator130 and a main pressure sensor 132. The accumulator 130 is an energystorage device in which the non-compressible hydraulic fluid 102 is heldunder pressure by an external source. In the example provided, theaccumulator 130 is a spring type or gas filled type accumulator having aspring or compressible gas that provides a compressive force on thehydraulic fluid 102 within the accumulator 130. However, it should beappreciated that the accumulator 130 may be of other types, such as agas-charged type, without departing from the scope of the presentinvention. Accordingly, the accumulator 130 is operable to supplypressurized hydraulic fluid 102 back to the main supply line 126.However, upon discharge of the accumulator 130, the second check valve124 prevents the pressurized hydraulic fluid 102 from returning to thepump 106. The accumulator 130, when charged, effectively replaces thepump 106 as the source of pressurized hydraulic fluid 102, therebyeliminating the need for the pump 106 to run continuously. The mainpressure sensor 132 reads the pressure of the hydraulic fluid 102 withinthe main supply line 126 in real time and provides this data to thetransmission control module 32. Accordingly, the transmission controlmodule 32 can operate the pump 106 based on real-time conditions of theaccumulator 130.

The main supply line 126 is channeled through a heat sink 134 used tocool the controller 32, though it should be appreciated that the heatsink 134 may be located elsewhere or removed from the hydraulic controlsystem 100 without departing from the scope of the present invention.The main supply line 126 supplies pressurized hydraulic fluid 102 tofour pressure control devices including a first clutch pressure controldevice 136, a second clutch pressure control device 138, and a firstactuator pressure control device 140, and a second actuator pressurecontrol device 141.

The first clutch pressure control device 136 is preferably anelectrically controlled variable force solenoid having an internalclosed loop pressure control. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thefirst clutch pressure control device 136 is operable to control thepressure of the hydraulic fluid 102. The first clutch pressure controldevice 136 includes an inlet port 136A that communicates with an outletport 136B when the first clutch pressure control device 136 is activatedor energized and includes an exhaust port 136C that communicates withthe outlet port 136B when the first clutch pressure control device 136is inactive or de-energized. Variable activation of the first clutchpressure control device 136 regulates or controls the pressure of thehydraulic fluid 102 as the hydraulic fluid 102 communicates from theinlet port 136A to the outlet port 136B. The internal closed looppressure control provides pressure feedback within the solenoid toadjust the amount of flow to the outlet port 136B based on a particularcurrent command from the controller 32, thereby controlling pressure.The inlet port 136A is in communication with the main supply line 126.The outlet port 136B is in communication with an intermediate line 142.The exhaust port 136C is in communication with the sump 104 or anexhaust backfill circuit (not shown).

The intermediate line 142 communicates the hydraulic fluid 102 from thefirst clutch pressure control device 136 to a first clutch flow controldevice 144, to a first pressure limit control valve 146, and a three wayball check valve 147. The first clutch flow control device 144 ispreferably an electrically controlled variable force solenoid that isoperable to control a flow of the hydraulic fluid 102 from the firstclutch flow control device 144 in order to actuate the first torquetransmitting device 22, as will be described in greater detail below.The first clutch flow control device 144 includes an inlet port 144Athat communicates with an outlet port 144B when the first clutch flowcontrol device 144 is energized to a current greater than a null pointcurrent (i.e., the zero forward/reverse flow point for the givencurrent) and includes an exhaust port 144C that communicates with theoutlet port 144B when the first clutch flow control device 144 isde-energized to a current less than the null point current. Variableactivation of the first clutch flow control device 144 regulates orcontrols the flow of the hydraulic fluid 102 as the hydraulic fluid 102communicates from the inlet port 144A to the outlet port 144B. The inletport 144A is in communication with the intermediate line 142. The outletport 144B is in communication with a first clutch supply line 148 and aflow restriction orifice 150. The exhaust port 144C is in communicationwith the sump 104 or an exhaust backfill circuit (not shown). The firstpressure limit control valve 146 is disposed in parallel with the firstclutch flow control solenoid 144 and is in communication with the firstclutch supply line 148. If pressure within the first clutch supply line148 exceeds a predetermined value, the first pressure limit controlvalve 146 opens to relieve and reduce the pressure.

The first clutch supply line 148 is in fluid communication with aninlet/outlet port 152A in a first clutch piston assembly 152. The firstclutch piston assembly 152 includes a single acting piston 154 slidablydisposed in a cylinder 156. The piston 154 translates under hydraulicpressure to engage the first torque transmitting device 22, shown inFIG. 1. When the first clutch flow control device 144 is activated orenergized, a flow of pressurized hydraulic fluid 102 is provided to thefirst clutch supply line 148. The flow of pressurized hydraulic fluid102 is communicated from the first clutch supply line 148 to the firstclutch piston assembly 152 where the pressurized hydraulic fluid 102translates the piston 154, thereby engaging the first torquetransmitting device 22. When the first clutch flow control solenoid 144is de-energized, the inlet port 144A is closed and hydraulic fluid fromthe cylinder 156 passes from the outlet port 144B to the exhaust port144C and into the sump 104 or an exhaust backfill circuit (not shown),thereby disengaging the first torque transmitting device 22. Thetranslation of the piston 154 is monitored by a position sensor 157.

The second clutch pressure control device 138 is preferably anelectrically controlled variable force solenoid having an internalclosed loop pressure control. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thesecond clutch pressure control device 138 is operable to control thepressure of the hydraulic fluid 102. The second clutch pressure controldevice 138 includes an inlet port 138A that communicates with an outletport 138B when the second clutch pressure control device 138 isactivated or energized and includes an exhaust port 138C thatcommunicates with the outlet port 138B when the second clutch pressurecontrol device 138 is inactive or de-energized. Variable activation ofthe second clutch pressure control device 138 regulates or controls thepressure of the hydraulic fluid 102 as the hydraulic fluid 102communicates from the inlet port 138A to the outlet port 138B. Theinternal closed loop pressure control provides pressure feedback withinthe solenoid to adjust the amount of flow to the outlet port 1388 basedon a particular current command from the controller 32, therebycontrolling pressure. The inlet port 138A is in communication with themain supply line 126. The outlet port 138B is in communication with anintermediate line 158. The exhaust port 138C is in communication withthe sump 104 or an exhaust backfill circuit (not shown).

The intermediate line 158 communicates the hydraulic fluid 102 from thesecond clutch pressure control device 138 to a second clutch flowcontrol device 160, to a second pressure limit control valve 162, and tothe three-way ball check valve 147. The second clutch flow controldevice 160 is preferably an electrically controlled variable forcesolenoid that is operable to control a flow of the hydraulic fluid 102from the second clutch flow control device 160 in order to actuate thesecond torque transmitting device 24, as will be described in greaterdetail below. The second clutch flow control device 160 includes aninlet port 160A that communicates with an outlet port 160B when thesecond clutch flow control device 160 is energized to a current greaterthan the null point current and includes an exhaust port 160C thatcommunicates with the outlet port 160B when the second clutch flowcontrol device 160 is de-energized below the null point current.Variable activation of the second clutch flow control device 160regulates or controls the flow of the hydraulic fluid 102 as thehydraulic fluid 102 communicates from the inlet port 160A to the outletport 160B. The inlet port 160A is in communication with the intermediateline 158. The outlet port 160B is in communication with a second clutchsupply line 164 and a flow restriction orifice 166. The exhaust port160C is in communication with the sump 104 or an exhaust backfillcircuit (not shown). The second pressure limit control valve 162 isdisposed in parallel with the second clutch flow control solenoid 160and is in communication with the second clutch supply line 164. Ifpressure within the second clutch supply line 164 exceeds apredetermined value, the second pressure limit control valve 162 opensto relieve and reduce the pressure. The translation of the piston 170 ismonitored by a position sensor 167.

The second clutch supply line 164 is in fluid communication with aninlet/outlet port 168A in a second clutch piston assembly 168. Thesecond clutch piston assembly 168 includes a single acting piston 170slidably disposed in a cylinder 172. The piston 170 translates underhydraulic pressure to engage the second torque transmitting device 24,shown in FIG. 1. When the second clutch flow control device 160 isactivated or energized, a flow of pressurized hydraulic fluid 102 isprovided to the second clutch supply line 164. The flow of pressurizedhydraulic fluid 102 is communicated from the second clutch supply line164 to the second clutch piston assembly 168 where the pressurizedhydraulic fluid 102 translates the piston 170, thereby engaging thesecond torque transmitting device 24. When the second clutch flowcontrol solenoid 160 is de-energized, the inlet port 160A is closed andhydraulic fluid from the cylinder 172 passes from the outlet port 160Bto the exhaust port 160C and into the sump 104 or an exhaust backfillcircuit (not shown), thereby disengaging the second torque transmittingdevice 24.

The three-way ball check valve 147 includes three ports 147A, 147B, and147C. The ball check valve 147 closes off whichever of the ports 147Aand 147B that is delivering the lower hydraulic pressure and providescommunication between whichever of the ports 147A and 147B having ordelivering the higher hydraulic pressure with the outlet port 147C. Theports 147A and 147B each communicate with the pressure control devices136 and 138, respectively. The outlet port 147C is in communication witha control device feed line 173. The control device feed line 173communicates with a valve control device 174. Accordingly, activation ofeither clutch pressure control devices 136 and 138 provides a flow ofpressurized hydraulic fluid 102 to the valve control device 174 via thecontrol device feed line 173 without allowing a flow of pressurizedhydraulic fluid 102 into the circuit of the inactivated clutch pressurecontrol device 136, 138.

The first and second pressure control devices 140 and 141 are operableto selectively provide flows of pressurized hydraulic fluid 102 throughfirst and second flow control devices 178, 180 and through first andsecond valve assemblies 182, 184 in order to selectively actuate aplurality of synchronizer shift actuators. The synchronizer actuatorsinclude a first synchronizer actuator 186A, a second synchronizeractuator 186B, a third synchronizer actuator 186C, and a fourthsynchronizer actuator 186D.

For example, the first actuator pressure control device 140 ispreferably an electrically controlled variable force solenoid having aninternal closed loop pressure control. Various makes, types, and modelsof solenoids may be employed with the present invention so long as thefirst actuator pressure control device 140 is operable to control thepressure of the hydraulic fluid 102. The first actuator pressure controldevice 140 includes an inlet port 140A that communicates with an outletport 140B when the first actuator pressure control device 140 isactivated or energized and includes an exhaust port 140C thatcommunicates with the outlet port 140B when the first actuator pressurecontrol device 140 is inactive or de-energized. Variable activation ofthe first actuator pressure control device 140 regulates or controls thepressure of the hydraulic fluid 102 as the hydraulic fluid 102communicates from the inlet port 140A to the outlet port 140B. Theinternal closed loop pressure control provides pressure feedback withinthe solenoid to adjust the amount of flow to the outlet port 140B basedon a particular current command from the controller 32, therebycontrolling pressure. The inlet port 140A is in communication with themain supply line 126. The outlet port 140B is in communication with anintermediate line 188. The exhaust port 140C is in communication withthe sump 104 or an exhaust backfill circuit (not shown).

The intermediate line 188 communicates pressurized hydraulic fluid 102from the first actuator pressure control device 140 to a first flowcontrol device 178 and the first valve assembly 182. The first flowcontrol device 178 includes an inlet port 178A that communicates throughan adjustable hydraulic orifice or restriction with an outlet port 1788when the first flow control device 178 energized to a current greaterthan the null point current and includes an exhaust port 178C thatcommunicates with the outlet port 178B when the first flow controldevice 178 is de-energized to a current less than the null pointcurrent. Variable activation of the first flow control device 178regulates or controls the flow of the hydraulic fluid 102 as thehydraulic fluid 102 communicates from the inlet port 178A to the outletport 178B. The inlet port 178A is in communication with the intermediateline 188. The outlet port 178B is in communication with an intermediateline 190 which communicates with the first valve assembly 182. Theexhaust port 178C is in communication with the sump 104 or an exhaustbackfill circuit (not shown).

The first valve assembly 182 is operable to selectively direct thepressurized hydraulic fluid 102 flows from the first pressure controldevice 140 and the first actuator flow control device 178 to the firstsynchronizer actuator 186A and to the second synchronizer actuator 186B,as will be described in greater detail below. The first valve assembly182 includes a first inlet port 182A, a second inlet port 182B, a firstoutlet port 182C, a second outlet port 182D, a third outlet port 182E, afourth outlet port 182F, a plurality of exhaust ports 182G, and acontrol port 182H. The first inlet port 182A is in communication withthe intermediate line 190. The second inlet port 182B is incommunication with the intermediate line 188. The first outlet port 182Cis in communication with a synchronizer supply line 192. The secondoutlet port 182D is in communication with a synchronizer supply line194. The third outlet port 182E is in communication with a synchronizersupply line 196. The fourth outlet port 182F is in communication with asynchronizer supply line 198. The exhaust ports 182G are ultimately incommunication with the sump 104 or an exhaust backfill circuit (notshown). The control port 182H is in communication with a control line200 that communicates with the control device 174.

The valve control device 174 is preferably an on-off solenoid that isnormally closed. However, it should be appreciated that other types ofsolenoids and other control devices may be employed without departingfrom the scope of the present invention, such as a pressure controlsolenoid. For example, the valve control device 174 may be a directacting solenoid. The valve control device 174 includes an inlet port174A in fluid communication with the control device feed line 173 and anoutlet port 174B in fluid communication with the control line 200. Thevalve control device 174 is electrically actuated by the controller 32between a closed state and an open state. In the closed state, the inletport 174A is prevented from communicating with the outlet port 174B. Inthe open state, the inlet port 174A is allowed to communicate with theoutlet port 1748.

The first valve assembly 182 further includes a valve spool 202 slidablydisposed within a valve body or bore 204. The valve spool 202 ismoveable between at least two positions by a biasing member 206 and byfluid flow channeled from the control device 174 via control line 200.The biasing member 206 is preferably a spring and acts on an end of thevalve spool 202 to bias the valve spool 202 to the first position orde-stroked position. When the control device 174 is energized oractivated a flow of the hydraulic fluid 102 is communicated to thecontrol port 182H via control line 200 and into a control chamber 191 ofvalve assembly 182. The hydraulic fluid 102 acts on an end of the valvespool 202 to move the valve spool 202 and compress biasing member 206 toplace valve spool 202 in the second position or stroked position. Asupply of pressurized hydraulic fluid is provided to the control device174 via intermediate fluid line 142 when the clutch pressure controldevice 136 is energized or opened.

When the valve spool 202 is in the de-stroked position, the first inletport 182A is in communication with the second outlet port 182D, thesecond inlet port 182B is in communication with the fourth outlet port182F, and the first and third outlet ports 182C, 182E are incommunication with the exhaust ports 182G. When the valve 202 is in thestroked position, as shown in FIG. 2B, the first inlet port 182A is incommunication with the first outlet port 182C, the second inlet port182B is in communication with the third outlet port 182E, and the secondand fourth outlet ports 182D, 182F are in communication with the exhaustports 182G. Accordingly, when the valve control device 174 is opened,pressurized hydraulic fluid 102 flows from the first pressure controldevice 140 and a variable flow of hydraulic fluid 102 flows from thefirst flow control device 178 to the second synchronizer actuator 186B.When the valve control device 174 is closed, pressurized hydraulic fluid102 flows from the first pressure control device 140 and a variable flowof hydraulic fluid 102 flows from the first flow control device 178 tothe first synchronizer actuator 186A.

The second actuator pressure control device 141 is preferably anelectrically controlled variable force solenoid having an internalclosed loop pressure control. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thesecond actuator pressure control device 141 is operable to control thepressure of the hydraulic fluid 102. The second actuator pressurecontrol device 141 includes an inlet port 141A that communicates with anoutlet port 141B when the second actuator pressure control device 141 isactivated or energized and includes an exhaust port 141C thatcommunicates with the outlet port 141B when the second actuator pressurecontrol device 141 is inactive or de-energized. Variable activation ofthe second actuator pressure control device 141 regulates or controlsthe pressure of the hydraulic fluid 102 as the hydraulic fluid 102communicates from the inlet port 141A to the outlet port 141B. Theinternal closed loop pressure control provides pressure feedback withinthe solenoid to adjust the amount of flow to the outlet port 141B basedon a particular current command from the controller 32, therebycontrolling pressure. The inlet port 141A is in communication with themain supply line 126. The outlet port 141B is in communication with anintermediate line 210. The exhaust port 141C is in communication withthe sump 104 or an exhaust backfill circuit (not shown).

The intermediate line 210 communicates pressurized hydraulic fluid 102from the second actuator pressure control device 141 to the second flowcontrol device 180 and the second valve assembly 184. The second flowcontrol device 180 is preferably an electrically controlled variableforce solenoid. Various makes, types, and models of solenoids may beemployed with the present invention so long as the second flow controldevice 180 is operable to control the flow of the hydraulic fluid 102.The second flow control device 180 includes an inlet port 180A thatcommunicates through an adjustable hydraulic orifice or restriction withan outlet port 1808 when the second flow control device 180 is energizedto a current above the null point current and includes an exhaust port180C that communicates with the outlet port 180B when the second flowcontrol device 180 is de-energized below the null point current.Variable activation of the second flow control device 180 regulates orcontrols the flow of the hydraulic fluid 102 as the hydraulic fluid 102communicates from the inlet port 180A to the outlet port 180B. The inletport 180A is in communication with the intermediate line 210. The outletport 180B is in communication with an intermediate line 212 whichcommunicates with the second valve assembly 184. The exhaust port 180Cis in communication with the sump 104 or an exhaust backfill circuit(not shown).

The second valve assembly 184 is operable to selectively direct thepressurized hydraulic fluid 102 flows from the second pressure controldevice 141 and the second actuator flow control device 180 to the thirdsynchronizer actuator 186C and to the fourth synchronizer actuator 186D,as will be described in greater detail below. The second valve assembly184 includes a first inlet port 184A, a second inlet port 184B, a firstoutlet port 184C, a second outlet port 184D, a third outlet port 184E, afourth outlet port 184F, a plurality of exhaust ports 184G, and acontrol port 184H. The first inlet port 184A is in communication withthe intermediate line 212. The second inlet port 184B is incommunication with the intermediate line 210. The first outlet port 184Cis in communication with a synchronizer supply line 214. The secondoutlet port 184D is in communication with a synchronizer supply line216. The third outlet port 184E is in communication with a synchronizersupply line 218. The fourth outlet port 184F is in communication with asynchronizer supply line 220. The exhaust ports 184G are incommunication with the sump 104 or an exhaust backfill circuit (notshown). The control port 184H is in communication with the control line200 that communicates with the control device 174.

The second valve assembly 184 further includes a valve spool 222slidably disposed within a valve body or bore 224. The valve spool 222is moveable between at least two positions by a biasing member 226 andby fluid flow channeled from the control device 174 via control line200. The biasing member 226 is preferably a spring and acts on an end ofthe valve spool 222 to bias the valve spool 222 to the first position orde-stroked position. When the control device 174 is energized oractivated a flow of the hydraulic fluid 102 is communicated to thecontrol port 184H via control line 200 and into a control chamber 227 ofvalve assembly 184. The hydraulic fluid 102 acts on an end of the valvespool 222 to move the valve spool 222 and compress biasing member 226 toplace valve spool 222 in the second position or stroked position. Itshould be appreciated that the valve control device 174 actuates bothvalve assemblies 182 and 184 when in the open condition via the controlline 200.

When the valve 222 is in the de-stroked position, the first inlet port184A is in communication with the second outlet port 184D, the secondinlet port 184B is in communication with the fourth outlet port 184F,and the first and third outlet ports 184C, 184E are in communicationwith the exhaust ports 184G. When the valve 222 is in the strokedposition, as shown in FIG. 2B, the first inlet port 184A is incommunication with the first outlet port 184C, the second inlet port184B is in communication with the third outlet port 184E, and the secondand fourth outlet ports 184D, 184F are in communication with the exhaustports 184G. Accordingly, when the valve control device 174 is opened,pressurized hydraulic fluid 102 flows from the second pressure controldevice 141 and a variable flow of hydraulic fluid 102 flows from thesecond flow control device 180 to the fourth synchronizer actuator 186D.When the valve control device 174 is closed, pressurized hydraulic fluid102 flows from the second pressure control device 141 and a variableflow of hydraulic fluid 102 flows from the second flow control device180 to the third synchronizer actuator 186C.

The synchronizer actuators 186A-D are preferably two-area pistonassemblies operable to each engage or actuate a shift rail in asynchronizer assembly, but can be three-area piston assemblies withoutdeparting from the scope of the present invention. For example, thefirst synchronizer actuator 186A is operable to actuate the firstsynchronizer assembly 30A, the second synchronizer actuator 186B isoperable to actuate the second synchronizer assembly 30B, the thirdsynchronizer actuator 186C is operable to actuate the third synchronizerassembly 30C, and the fourth synchronizer actuator 186D is operable toactuate the fourth synchronizer assembly 30D.

The first synchronizer actuator 186A includes a piston 230A slidablydisposed within a piston housing or cylinder 232A. A detent spring 231Abiases the piston 230A in a first engaged position, a second engagedposition and in a neutral position. The piston 230A presents twoseparate areas for pressurized hydraulic fluid to act upon. The piston230A engages or contacts a finger lever, shift fork, or other shift railcomponent 233A of the first synchronizer assembly 30A. The firstsynchronizer actuator 186A includes a fluid port 234A that communicateswith a first end 235A of the piston 230A and a fluid port 236A thatcommunicates with an opposite second end 237A of the piston 230A havinga smaller contact area than the first end 235A. Fluid port 234A is incommunication with the synchronizer supply line 194 and fluid port 236Ais in communication with the synchronizer supply line 198. Accordingly,the pressurized hydraulic fluid 102 communicated from the first actuatorpressure control device 140 enters the first synchronizer actuator 186Athrough the fluid port 236A and contacts the second end 237A of thepiston 230A and the flow of hydraulic fluid 102 from the first flowcontrol device 178 enters the first synchronizer actuator 186A throughthe fluid port 234A and contacts the first end 235A of the piston 230A.The difference in the force generated by the pressure of the hydraulicfluid 102 delivered to fluid port 236A from the first actuator pressurecontrol device 140 and the hydraulic fluid 102 delivered to fluid port234A from the first flow control device 178 moves the piston 230Abetween various positions. By controlling the flow of hydraulic fluid102 from the first flow control device 178, the piston 234A is actuatedbetween the various positions. Each position in turn corresponds to aposition of the shift rail of the first synchronizer assembly 30A (i.e.,engaged left, engaged right, and neutral). A fork position sensor 240Amay be included to communicate to the controller 32 the position of theshift fork 233A.

The second synchronizer actuator 186B includes a piston 230B slidablydisposed within a piston housing or cylinder 232B. A detent spring 231Bbiases the piston 230B in a first engaged position, a second engagedposition and in a neutral position. The piston 230B presents twoseparate areas for pressurized hydraulic fluid to act upon. The piston230B engages or contacts a finger lever, shift fork, or other shift railcomponent 233B of the second synchronizer assembly 30B. The secondsynchronizer actuator 186B includes a fluid port 234B that communicateswith a first end 235B of the piston 230B and a fluid port 236B thatcommunicates with an opposite second end 237B of the piston 230B havinga smaller contact area than the first end 235B. Fluid port 234B is incommunication with the synchronizer supply line 192 and fluid port 236Bis in communication with the synchronizer supply line 196. Accordingly,the pressurized hydraulic fluid 102 communicated from the first actuatorpressure control device 140 enters the second synchronizer actuator 186Bthrough the fluid port 236B and contacts the second end 237B of thepiston 230B and the flow of hydraulic fluid 102 from the first flowcontrol device 178 enters the second synchronizer actuator 186B throughthe fluid port 234B and contacts the first end 235B of the piston 230B.The difference in the force generated by the pressure of the hydraulicfluid 102 delivered to fluid port 236B from the first actuator pressurecontrol device 140 and the hydraulic fluid 102 delivered to fluid port234B from the first flow control device 178 moves the piston 230Bbetween various positions. By controlling the flow of hydraulic fluid102 from the first flow control device 178, the piston 234B is actuatedbetween the various positions. Each position in turn corresponds to aposition of the shift rail of the second synchronizer assembly 30B(i.e., engaged left, engaged right, and neutral). A fork position sensor240B may be included to communicate to the controller 32 the position ofthe shift fork 233B.

The third synchronizer actuator 186C includes a piston 230C slidablydisposed within a piston housing or cylinder 232C. A detent spring 231Cbiases the piston 230C in a first engaged position, a second engagedposition and in a neutral position. The piston 230C presents twoseparate areas for pressurized hydraulic fluid to act upon. The piston230C engages or contacts a finger lever, shift fork, or other shift railcomponent 233C of the third synchronizer assembly 30C. The thirdsynchronizer actuator 186C includes a fluid port 234C that communicateswith a first end 235C of the piston 230C and a fluid port 236C thatcommunicates with an opposite second end 237C of the piston 230C havinga smaller contact area than the first end 235C. Fluid port 234C is incommunication with the synchronizer supply line 216 and fluid port 236Cis in communication with the synchronizer supply line 220. Accordingly,the pressurized hydraulic fluid 102 communicated from the secondactuator pressure control device 141 enters the third synchronizeractuator 186C through the fluid port 236C and contacts the second end237C of the piston 230C and the flow of hydraulic fluid 102 from thesecond flow control device 180 enters the third synchronizer actuator186C through the fluid port 234C and contacts the first end 235C of thepiston 230C. The difference in the force generated by the pressure ofthe hydraulic fluid 102 delivered to fluid port 236C from the secondactuator pressure control device 141 and the hydraulic fluid 102delivered to fluid port 234C from the second flow control device 180moves the piston 230C between various positions. By controlling the flowof hydraulic fluid 102 from the second flow control device 180, thepiston 234C is actuated between the various positions. Each position inturn corresponds to a position of the shift rail of the thirdsynchronizer assembly 30C (i.e., engaged left, engaged right, andneutral). A fork position sensor 240C may be included to communicate tothe controller 32 the position of the shift fork 233C.

The fourth synchronizer actuator 186D includes a piston 230D slidablydisposed within a piston housing or cylinder 232D. A detent spring 231Dbiases the piston 230D in a first engaged position, a second engagedposition and in a neutral position. The piston 230D presents twoseparate areas for pressurized hydraulic fluid to act upon. The piston230D engages or contacts a finger lever, shift fork, or other shift railcomponent 233D of the fourth synchronizer assembly 30D. The fourthsynchronizer actuator 186D includes a fluid port 234D that communicateswith a first end 235D of the piston 230D and a fluid port 236D thatcommunicates with an opposite second end 237D of the piston 230D havinga smaller contact area than the first end 235D. Fluid port 234D is incommunication with the synchronizer supply line 214 and fluid port 236Dis in communication with the synchronizer supply line 218. Accordingly,the pressurized hydraulic fluid 102 communicated from the secondactuator pressure control device 141 enters the fourth synchronizeractuator 186D through the fluid port 236D and contacts the second end237D of the piston 230D and the flow of hydraulic fluid 102 from thesecond flow control device 180 enters the fourth synchronizer actuator186D through the fluid port 234D and contacts the first end 235D of thepiston 230D. The difference in the force generated by the pressure ofthe hydraulic fluid 102 delivered to fluid port 236D from the secondactuator pressure control device 141 and the hydraulic fluid 102delivered to fluid port 234D from the second flow control device 180moves the piston 230D between various positions. By controlling the flowof hydraulic fluid 102 from the second flow control device 180, thepiston 234A is actuated between the various positions. Each position inturn corresponds to a position of the shift rail of the fourthsynchronizer assembly 30D (i.e., engaged left, engaged right, andneutral). A fork position sensor 240D may be included to communicate tothe controller 32 the position of the shift fork 233D.

During general operation of the hydraulic control system 100, theaccumulator 130 provides the pressurized hydraulic fluid 102 throughoutthe system and the pump 106 is employed to charge the accumulator 130.Selection of a particular forward or reverse gear ratio is achieved byfirst selectively actuating one of the synchronizer assemblies 30A-D andthen selectively actuating one of the torque transmitting devices 22,24. It should be appreciated that the combination of selectiveengagement of the actuator assemblies 30A-D and torque transmittingdevices 22, 24 providing a forward or reverse gear ratio may varywithout departing from the scope of the present invention.

Generally, the first actuator pressure control device 140 selectivelyprovides pressurized hydraulic fluid 102 to each of the synchronizeractuators 186A-B and the first flow control device 178 and the secondactuator pressure control device 141 selectively provides pressurizedhydraulic fluid 102 to each of the synchronizer actuators 186C-D and thesecond flow control device 180. Individual synchronizer actuators 186A-Dare actuated by controlling a flow from one of the flow control devices178 and 180 based upon positioning of the first and second valveassemblies 182 and 184.

For example, to actuate the first synchronizer assembly 30A, the firstpressure control device 140 is energized to provide a pressure on thepiston 230A and to provide a flow of pressurized hydraulic fluid 102 tothe first flow control device 178. Bi-directional translation of thefirst synchronizer assembly 30A is then achieved by selectivelyenergizing the first flow control device 178. To actuate the secondsynchronizer assembly 30B, the first pressure control device 140 isenergized to provide a pressure force on the piston 230B and to providea flow of pressurized hydraulic fluid 102 to the first flow controldevice 178. Bi-directional translation of the second synchronizerassembly 30B is then achieved by selectively energizing the first flowcontrol device 178.

To actuate the third synchronizer assembly 30C, the second pressurecontrol device 141 is energized to provide a pressure force on thepiston 230C and to provide a flow of pressurized hydraulic fluid 102 tothe second flow control device 180. Bi-directional translation of thethird synchronizer assembly 30C is then achieved by selectivelyenergizing the second flow control device 180.

To actuate the fourth synchronizer assembly 30D, the second pressurecontrol device 141 is energized to provide a pressure force on thepiston 230D and to provide a flow of pressurized hydraulic fluid 102 tothe second flow control device 180. Bi-directional translation of thethird synchronizer assembly 30D is then achieved by selectivelyenergizing the second flow control device 180.

To engage or actuate the first torque transmitting device 22, the firstclutch pressure control device 136 and the first clutch flow controldevice 144 are energized or opened. To engage or actuate the secondtorque transmitting device 24, the second clutch pressure control device138 and the second clutch flow control device 160 are energized oropened.

Turning to FIG. 3, a method for controlling the oil delivery subsystem100A is generally indicated by reference number 300. Generally, theelectrically-driven, fixed displacement pump 106 is used to providepressurized hydraulic fluid 102 to be used to actuate the clutches 22,24 and synchronizers 30A-D to make the transmission 10 shift. Thehydraulic control system 100 provides this pressurized fluid 102independent of whether the engine (not shown) is running, therebykeeping the clutches 22, 24 staged for quick response during enginestart/stop maneuvers and other driving conditions. The pump 106 isturned on when the pressure sensor 132 indicates that the accumulator130 needs recharged and is turned off when full charge pressure isachieved.

Prior to initial charging of the hydraulic control system 100, theaccumulator 130 is depressurized. This provides no reserve hydraulicfluid 102 volume to be used by the transmission 10 for shifting.Therefore, the pressure sensor 132 sends a signal to the controller 32to start the pump 106 at step 302. At step 304 the pump 106 acceleratesto a fixed rpm and begins displacing hydraulic fluid 102 from the sump104, out through the oil filter 118 and check ball 120, and into theaccumulator 130 and the rest of the hydraulic control system 100. Thishydraulic fluid 102 builds pressure and begins to charge the accumulator130, indicated by line section 305 in FIG. 4. At step 306, the pressuresensor 132 senses the pressure of the hydraulic fluid 102 within fluidline 126 and therefore within the accumulator 130 and communicates thesensed pressure to the controller 32. At step 308 the sensed pressure iscompared to a first threshold value. The first threshold value is apredetermined pressure value indicative of a fully charged accumulator130, indicated by “P1” in the accumulator pressure versus time graphillustrated in FIG. 4. If the sensed pressure is less than the firstthreshold value the method 300 returns to step 306. If the sensedpressure is greater than or equal to the first threshold value, themethod 300 proceeds to step 310 where the current to the pump 106 isterminated by the controller 32 thereby causing the pump 106 to stopspinning. At this point hydraulic fluid 102 wants to rush from theaccumulator 130 back into the pump 106 but is prevented from doing so bythe check ball 124 which seats and seals the pump 106 from theaccumulator 130. With the check ball 124 seated, the only place for thehydraulic fluid 102 within the accumulator 130 to flow is to the rest ofthe subsystems 100B and 100C for clutch and synchronizer control.

However, the leakage of subsystems 100B and 100C and hydraulic fluid 102volume used to stroke actuators makes the pressure in the accumulator130 decrease over time, indicated by the line section 311 in FIG. 4. Atstep 312 the pressure sensor 132 senses the pressure of the hydraulicfluid 102 within fluid line 126 and therefore within the accumulator 130and communicates the sensed pressure to the controller 32. At step 314the sensed pressure is compared to a second threshold value. The secondthreshold value is a calculated pressure value in the accumulator 130that will guaranty sufficient accumulator reserve volume to accomplish anumber of rapid shifting maneuvers. The second threshold pressure isindicated by “P2” in the accumulator pressure versus time graphillustrated in FIG. 4. The accumulator reserve volume is a function ofthe number of shifts, the component volumes stroked, the shift times,the rate of system leakage, and the rate of pump output of thetransmission 10. The second threshold pressure is calculated as afunction of temperature, gas charge pressure in the accumulator 130,pump 106 output flow capabilities, either learned or assumed leakage andstroke volumes to engage or neutralize forks and clutches. The secondthreshold pressure is determined by calculating the accumulator pressurelevel that will guaranty the accumulator reserve volume. Once theaccumulator reserve volume is determined the pump restart pressure canbe calculated according to gas law physics. If the sensed pressure isgreater than or equal to the second threshold value the method 300returns to step 312. If the sensed pressure is less than the secondthreshold value, the method 300 proceeds to step 316 where the currentto the pump 106 is activated by the controller 32 thereby causing thepump 106 to restart. The method then returns to step 304 and the cyclecontinues, as shown in FIG. 4. The blow-off safety valve 116 is designedto unseat and limit the system pressure in the event that the pump 106does not shut off at the right time either due to a failed pump motor, afailed pressure sensor, or sluggish response. The designed blow-offpressure is slightly above the maximum expected system pressure. Forinstance if the maximum system pressure is 60 bar, the blow-off will bedesigned so the nominal may be at 80 bar.

The pump 106 may also run at a fixed lower rpm to create a closed-looppressure control during some failsafe operation modes where a failedclutch solenoid could result in over pressurization of the clutch 22 or24. The pump 106 can be turned on during shifting events whererelatively large amounts of hydraulic volume are extracted from theaccumulator 130. The pump 106 can also be turned on prior to the driverstarting the engine (not shown) to hydraulically charge the system 100before any shifting or drive-away is requested. Pre-start of the pump106 can be triggered by the opening of a door, unlocking of the cardoors, or other means.

Turning now to FIG. 5, a method for controlling the clutch controlsubsystem 100B is generally indicated by reference number 400. In thisembodiment, the even and odd clutch circuits (i.e. the fluid lines andsolenoids, and actuators that control the positions of the clutches 22,24) are identical but independent. Accordingly, reference to bothcircuits will be made hereinafter in discussing the method 400. However,each circuits' flow rate and clutch position can be independentlycommanded based on the specific shifting or staging needs of thatclutch. The method 400 begins at step 402 where the controller 32determines a target clutch torque for one of the clutches 22, 24. Thetarget clutch torque is an amount of torque required to perform anaction within the transmission 10, such as a shift event or maintaininga gear ratio. At step 404 the controller 32 uses a clutch torque toclutch actuator 152, 168 position relationship to determine a targetclutch position that will provide the target clutch torque. The clutchtorque to clutch actuator 152, 168 position relationship is learned asthe transmission 10 is operating by relating the reported engine torquewhile the clutches 22, 24 are slipping to the position of the pistons154, 170 reported by the clutch position sensors 157 and 167. Thisrelationship, once learned, is used to provide a feed-forward controlcommand while shifting. Closed-loop control is also used to fine tunethe relationship between the clutch torque to clutch actuator 152, 168position relationship.

At step 406 the controller 32 calculates a commanded pressure level ofthe pressure control solenoid 136, 138 that is selected to control theselected clutch 22, 24. The commanded pressure level of the selectedpressure control solenoid 136, 138 is calculated from the higher ofthree pressure requirements: the first pressure requirement is thepressure level required to enable the required amount of flow throughthe flow control solenoids 160 and 144; the second is the pressure levelrequired to hold the target clutch torque on the selected clutch 22, 24;and the third is the pressure level required to shift the mode valves182 and 184. In some cases a pressure drop required across flow controldevises 144 & 160 results in a pressure higher than the pressurerequired for clutch torque capacity. Once the commanded pressure levelis calculated, the method proceeds to step 408 where the controller 32sends a current to the selected pressure control solenoid 136, 138 toprovide the commanded pressure level. The selected pressure controlsolenoid 136, 138 has a performance characteristic that relatesregulated pressure to commanded electrical current. Once the commandedpressure level is determined, the appropriate amount of current can becommanded to the selected pressure control solenoid 136, 138. Thecommanded pressure level establishes an upstream side of a pressurepotential across the selected flow control solenoid 144, 160 that is incommunication with the selected pressure control solenoid 136, 138. Thecommanded pressure level for selected pressure control solenoids 136 and138, feeds a three way check valve assembly 147, in order to feed modevalve control solenoid 174. The higher pressure output, pressure controlsolenoid 136 or 138 toggles over the three way check ball to cut offfeed from the lower pressure control solenoid 136 or 138. The higherpressure oil from pressure control solenoid 136 or 138 then feedsthrough the three way check valve 147 to the mode valve control solenoid174. At step 410 the clutch position sensors 157, 167 sense the positionof the pistons 154, 170 of the clutch actuators 152, 168 andcommunicates the current position of the pistons 154, 170 to thecontroller 32. At step 411, the controller 32 determines a current sentto flow control devises 144 & 160 to achieve the targeted clutchposition determined in step 404. At step 412 the controller 32 uses apredetermined clutch actuator 152, 168 position to clutch pressurerelationship to estimate a current clutch pressure. At step 414 thecontroller 32 calculates the pressure potential across the selected flowcontrol solenoid 144, 160. The pressure potential across the selectedflow control solenoid 144, 160 is calculated by subtracting the currentclutch pressure from the commanded pressure level of the selectedpressure control solenoid 136, 138 (i.e. the upstream pressure potentialminus the downstream pressure potential).

Once the pressure potential across the selected flow control solenoid144, 160 has been determined, at step 416 the controller 32 determines,based on the pressure potential across the selected flow controlsolenoid 144, 160, whether to exhaust, maintain, or provide add pressureto hold a pressure drop across flow control solenoids 144 & 160 toprovide predictable flow rates to position the selected clutch 22, 24 tothe target clutch position determined in step 404 in order to providethe target clutch torque. The pressure potential supplied across theselected flow control solenoid 144, 160 creates a relationship betweenan electrical current and a flow rate from the selected flow controlsolenoid 144, 160. As described above, the flow control solenoids 144,160 are capable of both positive (feed) flow, zero flow, and negative(exhaust) flow depending on the value of current commanded. At step 418the controller 32 commands the proper current on the flow controldevices 144, 160 that will bring the current clutch position to thetarget clutch position. Closed loop control may also be used based onactual and commanded piston 154, 170 velocity and position to controlthe flow control solenoids 144, 160 At step 420, closed loop control isused by the controller 32 based on actual and commanded piston 180, 200velocity and position to control the flow control solenoids 160, 162. Ifthe current position of the piston 180, 200 does not equal the commandedposition of the piston 180,200, the method 400 returns to step 418. Ifthe current position of the piston 180, 200 does equal the commandedposition of the piston 180,200, the method 400 proceeds to step 422where the controller 32 stops the commanded current to the flow controldevices 160, 162. If the clutches 22, 24 are being engaged, flow ispositive and larger currents are commanded. If the clutches 22, 24 arebeing disengaged, flow is negative and lower currents are commanded.There is a region of current in the middle where the flow is deadheaded,neither feeding nor exhausting. Steps 402 through 418 are continuouslyprocessing to ensure that clutches 22 & 24 are in their proper position.

The spring loaded check balls 146, 162 may be provided to allow quickreleases of the clutches 22, 24 or to release the clutches 22, 24 in theevent of a flow control solenoid 144, 160 sticking in the deadheadedregion. The clutches 22, 24 are released through the check balls 146,162 by reducing the pressure control solenoids 136, 138 pressure belowthe clutch pressure level and check ball threshold. The pressure andflow rate to each clutch 22, 24 can be independently controlled based onthe specific shifting or staging needs of the clutches 22, 24.

Turning now to FIG. 6, the method of controlling the synchronizercontrol subsystem 100C is generally indicated by reference number 500.The synchronizer control subsystem 100C consists of two duplicatedhydraulic circuits to control the odd and even gear synchronizers,respectively. One circuit consists of one of the pressure controlsolenoids 140, 141, one of the flow control solenoids 178, 180, one ofthe mode valves 182, 184, the shared mode valve solenoid 174, and two ofthe actuators 186A-D. One circuit may control the 1st, 3rd, 5th, and 7thgear synchronizers, for example. The other circuit may control the 2nd,4th, 6th, and Reverse gear synchronizers, for example. Each forkactuator 233A-D is dual-acting meaning that it has a fully-engagedposition to the left, a neutral position in the middle, and a fullyengaged position to the right. For example, one actuator piston couldengage the 3rd gear synchronizer to the left and the 5th gearsynchronizer to the right with a neutral position in the middle.

The method 500 begins at step 502 where the controller 32 selects asynchronizer 30A-D to be engaged in order to meet the shiftingrequirements of the motor vehicle. The method 500 applies to anyselected synchronizer 30A-D, therefore reference to both of the odd andeven circuits will hereinafter be used. The synchronizers 30A-D operatein different modes, shown in FIG. 7. The synchronizer modes consist oftwo steady-state modes and at least three transient modes. Thesteady-state modes include a fully engaged mode 501 and a neutralizedmode or pre-staging 503. Transient modes consist of a pre-synchronizedmode 505, a synchronizing mode 507, and post-synchronized mode 509.Moreover, line “A” in FIG. 7 indicates the relative synchronizer forceover time, line “B” indicates the actual synchronizer position overtime, and line “C” indicates the fork position command over time.

Prior to any synchronizer shifting event, the mode valves must bepositioned to connect the pressure and flow control solenoids 140, 141and 178, 180, respectively, to the actuator 186A-D that controls theselected synchronizer 30A-D. Accordingly, the method 500 proceeds tostep 504 where the controller 32 sends an appropriate electric currentcommand to the mode valve solenoid 174. If the current command is high,the solenoid 174 will impart a pressure within the signal chambers 191and 227 at the head of the valves 202 and 222 of both mode valves 182and 184. This pressure is sufficient to move the valves 202 and 222against the bias springs 206 and 226, respectively. This will connectthe odd branch pressure control solenoid and the flow control solenoid,for example, to the 3rd and 5th gear actuator piston and the even branchpressure control solenoid and flow control solenoid, for example, to the2nd and 6th gear actuator piston. If the current command is low, themode valve solenoid 174 will exhaust the signal chambers 191 and 227 atthe head of the valves 202 and 222. This causes the bias springs 206 and226 to push the valves 202 and 222, respectively, to their de-energizedor de-stroked positions. This will connect the odd branch pressurecontrol solenoid and the flow control solenoid, for example, to the 1stand 7th gear actuator piston and the even branch pressure controlsolenoid and the flow control solenoid, for example, to the 4th andReverse gear actuator piston. Actual pairings of mode valve states,actuator pistons, and gear pairings per actuator 186A-D may vary withoutdeparting from the scope of the present invention.

As noted above, the actuator pistons 230A-D have two opposing areas235A-D and 237A-D of different size. The larger area is connected to theoutput of one of the flow control solenoids 178, 180. The smaller areais connected to one of the pressure control solenoid 140, 141 outputs.If one of the pistons 237A-D is desired to move to the right, theconnected pressure control solenoid 140, 141 is commanded to a pressurelevel and the connected flow control solenoid 178, 180 is commanded to aposition where the connected flow control solenoid 178, 180 will feedthe hydraulic fluid 102 from the connected pressure control solenoid140, 141 to the larger area of the actuator piston 230A-D. Pressurebuilds up in the larger area, and eventually an equilibrium force isreached. Beyond this equilibrium force the piston 230A-D will begin tomove to the right against the detent spring load and pressure controlsolenoid pressure force generated on the smaller opposing area. If theactuator 230A-D is desired to move to the left, the connected pressurecontrol solenoid 140, 141 is commanded to a pressure level and theconnected flow control solenoid 178, 180 is commanded to a positionwhere the connected flow control solenoid 178, 180 will exhaust thehydraulic fluid 102 in the larger area of the actuator piston 230A-D. Aspressure drops in the larger area, eventually an equilibrium force isreached. Beyond this equilibrium force the piston 230A-D will begin tomove to the left due to the detent spring 231A-D load and the connectedpressure control solenoid 140, 141 pressure force generated on thesmaller opposing area.

Once the mode valve assemblies 182 and 184 have been pre-staged, asshown at 503 in FIG. 7, the method 500 proceeds to step 506 where thecontroller 32 commands the pressure control solenoid 140, 141 to apredetermined pressure level. This step begins the pre-sync mode 505.The pre-sync mode 505 consists of moving the actuator piston 230A-D andfork 233A-D until the synchronizer sleeve (not shown) contacts theblocker ring (not shown) in the synchronizer 30A-D. The predeterminedpressure level is a pressure of the hydraulic fluid 102 sufficient toprovide a flow rate required to move the actuator piston to thecommanded position in the desired amount of time and to overcome thedetent spring and piston drag. At step 508 the flow control solenoid178, 180 is commanded to open to either feed or exhaust the larger areavolume, depending on the desired direction of movement of thesynchronizer 30A-D. These commands to the pressure control solenoids140, 141 and the flow control solenoids 178, 180 are adjusted asdictated by closed-loop position control using piston position andvelocity feedback from the position sensor at step 510.

At step 512 the controller determines whether the piston 230A-D isapproaching the learned position at which synchronization will begin. Ifthe piston 230A-D is not nearing the learned position, the methodreturns to step 510. If the piston 230A-D is approaching the learnedposition, the method proceeds to step 514 where the pressure from thepressure control solenoid 140, 141 is reduced in order to slow thevelocity of the piston 230A-D. Slowing the velocity of the piston 230A-Davoids a bump or clunk when synchronizer contact is made.

At step 516 the beginning of the synchronization mode 507 is signaledbased on piston position and shaft speed feedback from the speed sensors(not shown). Next, the flow control solenoid 178, 180 flow ratecommanded in or out is increased to reduce restriction in the circuit.This allows the controlling force on the piston 230A-D to be only afunction of the pressure control solenoid 140, 141. The actuator forcethrough the synchronization mode 507 is ramped to provide a smooth speedchange across the synchronizer without any clunks or bumps through usingpressure control solenoids 140 & 141. If the desired synchronizationforce is to the right, the flow control solenoid 178, 180 opens up tofeed the actuator 186A-D. Accordingly, the pressure on both sides of thepiston 230A-D is equalized, but since the larger area provides a largerforce than the smaller area, there is a net force to the right. If thedesired synchronization force is to the left, the flow control solenoid178, 180 opens up to exhaust. This drops the pressure on the large sideof the piston, but since the smaller area is still pressurized, there isa net force to the left.

At step 518 the controller 32 determines whether the synchronizationmode 507 is nearing the end. If the synchronization mode 507 is notnearing the end, the method returns to step 516. If the synchronizationmode 507 is nearing the end, pressure provided by the pressure controlsolenoid 140, 141 is lowered at step 520 in anticipation of thepost-sync mode 509.

At step 522 the controller 32 determines whether the post-sync mode 509has been signaled. The post-sync mode 509 begins when the blocker ring(not shown) indexes and allows the sleeve (not shown) of thesynchronizer 30A-D to move through to full engagement with the gear 26.If the post-sync mode 509 has not been signaled, the method 500 returnsto step 520. If the post-sync mode 509 has been signaled, the methodproceeds to step 524 where the velocity of the fork actuator 233A-D iscontrolled to avoid a clunk when the sleeve (not shown) contacts andstops on the gear 26. The velocity of the fork actuator 233A-D iscontrolled with closed-loop position and velocity control wherein apressure level is set with the pressure control solenoid 140, 141 andthe flow control solenoid 178, 180 is opened to either feed or exhaustto control the velocity of the piston 230A-D.

At step 526 the controller 32 determines whether the full engagementmode 501 has been signaled. The full engagement mode 501 begins when thesleeve (not shown) contacts and stops on the gear 26. If the fullengagement mode 501 has not been signaled, the method 500 returns tostep 524. If the full engagement mode 501 has been signaled, the methodproceeds to step 528 where the pressure control solenoid 140, 141pressure is profiled to zero pressure as active control of the flowcontrol solenoid 174, 180 is maintained. This guarantees that the fork233A-D remains in full engagement. Once the full engagement mode 501 iscomplete the mode valve solenoid 174 pressure is reduced to zero at step530 in order to conserve leakage at the head of the mode valves 202 and226. Back taper on the synchronizer teeth (not shown) and the detentspring force hold the synchronizer 30A-D in full engagement.

When disengaging the synchronizer 30A-D from full engagement mode backto neutral mode 503, there is only a position and velocity controlledphase. At step 532 the mode valve solenoid 174 is commanded to theappropriate state to couple the pairs of pressure control solenoids 140,141 and flow control solenoids 178, 180 to the appropriate actuator186A-D. At step 534 the flow control solenoid 178, 180 is opened eitherto feed or exhaust depending on the direction of the intended motion.The pressure control solenoid 140, 141 is commanded to a pressure levelrequired to generate the commanded flow across the flow control solenoid178, 180. Next, the flow control solenoid 178, 180 is commanded to flowoil into or out of the large area chamber at step 536, forcing thepiston 230A-D to move. The position and velocity of the actuator piston230A-D is controlled via closed-loop control using the feedback of theposition sensor 233A-D at step 538. As the fork 233A-D approaches themiddle neutral position, the commanded velocity is slowed at step 540.Once the piston 230A-D has reached a region near the learned neutralposition, the pressure control solenoid 140, 141 is profiled off whilestill actively controlling the flow control solenoid 178, 180 at step542. Once the pressure is exhausted on the actuator 230A-D, a mechanicaldetent spring (not shown) holds the actuator 230A-D in the neutralposition. The mode valve solenoid 174 is then commanded to zero pressureto conserve leakage at the head of the mode valves at step 544, and fulldisengagement is complete.

The components of the hydraulic control subsystem 100 are connected viaa plurality of fluid communication lines, as described above. It shouldbe appreciated that the fluid communication lines may be integrated in avalve body or formed from separate tubing or piping without departingfrom the scope of the present invention. In addition, the fluidcommunication lines may have any cross sectional shape and may includeadditional or fewer bends, turns, and branches than illustrated withoutdeparting from the scope of the present invention. The valve assemblydescribed above is illustrated as spool valve assembly having multipleports. However, it should be appreciated that other specific types ofvalves having greater or fewer ports may be provided without departingfrom the scope of the present invention. Finally, it should beappreciated that the source of pressurized hydraulic fluid, i.e. thepump accumulator 130 and the electrically driven pump 106 may bereplaced by alternate hydraulic fluid sources, such as an engine drivenpump.

By providing flow control of the clutches 22 and 24 and/or thesynchronizer assemblies 30A-D, the hydraulic control system 100 isoperable to provide direct clutch position control, direct synchronizeractuator position control, and variable clutch and synchronizer actuatorposition control. At the same time, quick clutch response times areenabled, spin losses are reduced, and packaging space of the hydrauliccontrol system 100 is reduced, all of which contributes to improved fueleconomy and performance. The hydraulic control system 100 is alsocompatible with BAS/BAS+ hybrid systems. Finally, failure modeprotection is enabled through pre-staged position control of the controldevices 136, 138, 140, 141, 144, 160, 178, 180, and the valves 182 and184.

The description of the invention is merely exemplary in nature andvariations that do not depart from the general essence of the inventionare intended to be within the scope of the invention. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention.

The invention claimed is:
 1. A method of controlling a dual clutch and aplurality of synchronizers in a transmission, the method comprising:selecting a synchronizer from the plurality of synchronizers and aclutch from the dual clutch to be actuated in order to achieve a desiredspeed ratio in the transmission; selecting a commanded pressure levelfor a clutch pressure control solenoid in upstream fluid communicationwith the selected clutch from the higher of a pressure level required toenable a required amount of flow through a clutch flow control solenoidin downstream fluid communication with the pressure control solenoid, apressure level required to hold a clutch torque on the selected clutch,and a pressure level required to position a mode valve from a firstposition and a second position; commanding the clutch pressure controlsolenoid to provide a first supply of hydraulic fluid at the selectedcommanded pressure level; commanding the clutch flow control solenoid toprovide a flow rate of the first supply of hydraulic fluid that willactuate the selected clutch; commanding a synchronizer pressure controlsolenoid to provide a second supply of hydraulic fluid to a synchronizerflow control solenoid and to a first input of the mode valve; commandingthe synchronizer flow control solenoid to provide a third supply ofhydraulic fluid to a second input of the mode valve; actuating the modevalve to one of the first and second positions to connect the firstinput with a first output and the second input with a second output,wherein the first output is connected to a first portion of a chamber ofa actuator and the second output is connected to a second portion of thechamber of the actuator; and modulating the second supply of hydraulicfluid from the synchronizer pressure control solenoid and the thirdsupply of hydraulic fluid from the synchronizer flow control solenoid tomove the actuator to a at least one of a first and second position toengage the selected synchronizer.
 2. The method of claim 1 wherein thestep of positioning the mode valve includes commanding a valve controlsolenoid in downstream fluid communication with the clutch pressurecontrol solenoid to provide a third supply of hydraulic fluid to themode valve.
 3. A method for controlling a dual clutch in a transmission,the dual clutch having a clutch actuatable by a clutch actuator, theclutch actuator in downstream fluid communication with a flow controlsolenoid that is in downstream fluid communication with a pressurecontrol solenoid, the method comprising: determining a target clutchtorque to be provided by the clutch; determining a target clutchposition of the clutch that will provide the target clutch torque usinga clutch torque to clutch actuator position relationship; selecting afirst pressure of a hydraulic fluid to be provided by the pressurecontrol solenoid from the higher of a pressure required to enable arequired amount of flow through the flow control solenoid to actuate theclutch, a pressure required to hold the target clutch torque on theclutch, and a pressure required to shift a mode valve; commanding thepressure control solenoid to provide a first supply of hydraulic fluidat the selected first pressure to establish an upstream side of apressure potential across the flow control solenoid; sensing a positionof the clutch actuator; estimating a second pressure of a second supplyof hydraulic fluid at the clutch actuator using a predetermined clutchactuator position to clutch pressure relationship; calculating apressure potential across the flow control solenoid by subtracting thesecond pressure from the first pressure, wherein the pressure potentialacross the flow control solenoid creates a relationship between acontrol signal and a flow rate from the flow control solenoid;determining a flow rate of the first supply of hydraulic fluid to beprovided by the flow control solenoid that will position the clutchactuator to the target clutch position; determining a control signal tobe sent to the flow control solenoid to provide the flow rate of thefirst supply of hydraulic fluid; and communicating the control signal tothe flow control solenoid to move the clutch actuator to the targetclutch position to provide the target clutch torque.
 4. The method ofclaim 3 further comprising the step of maintaining the pressurepotential across the flow control solenoid by commanding the pressurecontrol solenoid to exhaust, maintain, or provide added pressure to theflow control solenoid.
 5. The method of claim 3 wherein the targetclutch torque is an amount of torque required to perform an actionwithin the transmission including performing a shift event ormaintaining a gear ratio.
 6. The method of claim 3 wherein the clutchtorque to clutch actuator position relationship is learned as thetransmission is operating by relating a engine torque while the clutchis slipping to a position of the clutch actuator.
 7. The method of claim3 further comprising the step of adjusting the clutch torque to clutchactuator position relationship using closed-loop position control. 8.The method of claim 3 wherein step of sensing the clutch actuatorposition includes sensing the clutch actuator position using a clutchposition sensor.
 9. A method synchronizing a speed of a shaft to a gearin a transmission of a motor vehicle, the method comprising: monitoringa position of an actuator configured to move a synchronizer coupled tothe shaft; monitoring a speed of the shaft; positioning a mode valve toconnect a pressure control solenoid and a flow control solenoid with theactuator; determining an initial position of the synchronizer based onthe monitored position of the actuator; commanding the pressure controlsolenoid to provide a first supply of hydraulic fluid at a firstpredetermined pressure to the actuator and the flow control solenoid;commanding the flow control solenoid to either feed a second supply ofhydraulic fluid at a first flow rate to the actuator or to exhausthydraulic fluid from the actuator at the first flow rate depending on adesired direction of movement of the synchronizer in order to move thesynchronizer from the initial position to a first position; determiningwhether the synchronizer has reached the first position based on themonitored position of the actuator; reducing the pressure of the firstsupply of hydraulic fluid from the pressure control solenoid to a secondpredetermined pressure level when the synchronizer is moving between thefirst position and a second position in order to reduce a speed of theactuator; determining whether the synchronizer has reached the secondposition based on the monitored position of the actuator and themonitored speed of the shaft; commanding the flow control solenoid toeither feed or exhaust the actuator at a second flow rate that is lessthan the first flow rate when the actuator has reached the secondposition; increasing the pressure of the first supply of hydraulic fluidfrom the pressure control solenoid to a third predetermined pressurelevel when the synchronizer has reached the second position to move theactuator to a third position; determining whether the synchronizer hasreached the third position based on the monitored position of theactuator; reducing the pressure of the first supply of hydraulic fluidfrom the pressure control solenoid to a fourth predetermined pressurelevel when the synchronizer is moving between the third position and afourth position to reduce a speed of the actuator; determining whetherthe synchronizer has reached the fourth position based on the monitoredposition of the actuator; reducing the pressure of the first supply ofhydraulic fluid from the pressure control solenoid to a fifthpredetermined pressure level and commanding the flow control solenoid toeither feed or exhaust the actuator at a third flow rate when thesynchronizer is moving between the fourth position and a fifth position;determining whether the synchronizer has reached the fifth positionbased on the monitored position of the actuator; and commanding thepressure control solenoid to zero pressure when the synchronizer is atthe fifth position.
 10. The method of claim 9 wherein the first, second,third, fourth, and fifth predetermined pressure levels are each apressure sufficient to provide a flow rate required to move the actuatorto the commanded position in a desired amount of time and to overcome adetent spring and actuator drag.
 11. The method of claim 9 wherein thesecond position is the position of the synchronizer wherein asynchronizer sleeve contacts a blocker ring.
 12. The method of claim 11wherein the fourth position is a position wherein the blocker ringindexes with the gear and the synchronizer sleeve engages the gear. 13.The method of claim 12 wherein the fifth position is the position of thesynchronizer wherein the synchronizer couples the shaft to the gear. 14.The method of claim 13 wherein the first position is disposed betweenthe initial position and the first position.
 15. The method of claim 14wherein the third position is disposed between the second position andthe fourth position.
 16. The method of claim 9 wherein the step ofpositioning the mode valve includes commanding a pressure on a modevalve control solenoid, wherein the commanded pressure is sufficient tomove the mode valve and wherein movement of the mode valve connects thepressure control solenoid and the flow control solenoid to the actuatorof the synchronizer.
 17. The method of claim 9 wherein the commands onthe flow control solenoid and the pressure control solenoid are adjustedusing actuator position and velocity feedback.